FWIW my .028/.030 gapped 5.3 didn’t smoke noticeably or anything. But it did push much more oil out the breathers after a pass.

.028 is still .007 x the bore… plenty of gap IMO. I can’t imagine needing larger than .028 on a 4” bore.

 

If we're not talking about stock rings, I'd get my recommended ring gap from the ring manufacturer... If it were me.

I gaped both top & bottom between 0.028 & 0.030, stock rings and pistons, 5.3L.

Haven't run it yet, but my logic was to go big and eliminate any possible issue with butting. It's my first turbo build too, gonna have enough to worry about. One less thing now and can concentrate on "perfecting" it, if need be, some other time/project.

Again, that's just me.

Will have a vacuum pump on it too, so if there is a little extra blow-by... whatever.

 

.028 is where I was going to go on the top ring and .030 on the 2nd. I'm also not worried about a little blow by as long as its not too bad. I would rather be safe than sorry.

 

If you put a piston in a bore,

and apply heat as with a torch hot enough,


will the piston rings not eventually butt? With no movement, no boost, no compression, just heat it up and expand it to the point the ring ends butt.
Isn't it possible?

 

im not reading any of this ill just add i do 25 lower 28 upper, if i get greedy with the grinder sometimes i have a 30-32 upper, oh well. still make 750+

 

I read somewhere at one point, "stock" 5.3 ring gap is .015 top ring, .023 bottom ring. Is this accurate?

What are some of you 100% street car guys doing? Seems like most of the recommendations I ever see are from drag/street race guys (who probably don't care too much about oil consumption or blow-by)

What about those of us with 100% street cars that we don't want to have ridiculous amounts of blow-by just to be safe on the motor? There's certainly a happy medium, somewhere? I never see anybody talking about oil consumption or blow-by, just that their motors never blew up on a certain gap.

I mentally settled on a .006 x bore for the top ring and .0065 x bore for the bottom ring by aggregating a bunch of piston manufacturer data. So on a 5.3 that would be .02268 top ring and .02457 bottom ring.

Although I haven't run anything with this yet, just what I "plan" on running.

Am I understanding that you're making the top ring larger than the bottom ring? I thought typically it's recommended to do opposite of that?

Also, are all of you guys running E85? That's not an option by me...I'll be doing 93 octane + meth injection. Will that substantially change the ring gap recommendation?

 

Still don't understand the logic of having the second ring gap wider.

Anyone?

If they're the same material, I can't fathom any reasonable logic.

 

This is logic I can see

 

i have always done top ring wider because its the hottest right? closest to combustion?

this is easily a 40+ page argument,

but ive done turbo civics and turbo ls motors and i dont have problems with how i do it lol

 

I cant believe nobody posted yet the answer.

Second ring is loose because there have been instances where pressure between the top and second ring has torn the top of the piston off. So everyone runs a loose second ring to prevent this situation.

Now as to the gap vs durability. What I am getting at is, the piston will seize in the bore if you apply high temperature. When you overheat an engine, the parts can expand so much that cranking it over it no longer possible. So piston manufacturers often leave some room (their recommended piston/wall clearance) for the expansion of a piston at worst case scenario operating temperature (not overheating temperature). Which may be too much clearance for a street car, whos engine might not ever have that situation (it may require less than manufacturer recommended piston/wall clearance to adequate on the street). On the other hand, the ring is squeezed closed by combustion event, not specifically by the temperature increase. It doesnt matter how the extra air gets in there (from nitrous or turbo, you need the extra gap for the combustion pressure) so we see that ring gap is related to peak/worst case scenario condition for combustion pressure, not necessarily anything to do with piston/wall or temperature related situation.

For example,
An 6L engine which sees an extra atmosphere of boost pressure, well, even a tight OEM ring gap could probably handle this sort of torque (combustion pressure) without "seizing" or tearing up the piston. So I would not be so quick to gap an 500-600rwhp V8 engine much larger, if any, than a stock configuration would have it. A little for safety, sure, but to nearly double the OEM gap seems excessive. If the motor was going to see 30psi once in a while or a shot of nitrous then sure you need the headroom. But it comes at a cost.

 

wiseco says gap second wider to eliminate piston flutter .dont know if this applies to stock piston since skirt is a lot shorter

 

"McKnight says the optimal end gap for a top compression ring is when you achieve the smallest gap without butting the ends of the ring together when the rings get hot. “A good starting point for the top compression ring is .0045? per inch of bore diameter for a naturally aspirated engine, and .006? for a power adder application.

“The second ring end gap should be .005? to .010? wider than the top ring gap to prevent gas build up between the top and second rings. This can cause the top ring to flutter or bounce and lose its seal.”"

http://www.enginebuildermag.com/2011...ct-horsepower/

Over the years I have also read about how someone lost the top of a piston etc...
and there are misnomers all over the place, it says "for when piston rings get hot" but clearly the top temperature conditions are affecting piston diameter more than ring end butting. In a street application, use the longest rod possible, and the tightest piston possible with the tightest ring. Its pretty common sense you want it tight. The same goes for bearing clearance on an engine like that. This lowers potential redline, but thats the whole point in a street car /reliable daily driver is minimize rpm and maximize early torque, use a tight stall, and a power adder for sure to wrap things up.

If you are seriously building something then you need to communicate with the piston ring manufacturer AND the engine machinist, the two need to be on the same level, any miscommunication there and big problems.

 

i run a .030/.030 gap on mine. Has a little blow by on the breather tube but doesnt smoke or consume oil

 

I like all the replies on this topic. And most are saying the same thing with small variances to the actual gap, depending on what works for them or has worked in the past. That's great too. There doesn't seem to be a large discrepancy between the actual gap numbers more than .002 to.004 really.

On street only engines I always build them for tight piston clearance and tight ring gaps. But they don't see the heat, increased compression and added combustion levels that race engines do. On our race engines, these were always either NA or N2O specific. Both being about 15-1 compression ratio. On the Nitrous engines, they always get more piston clearance and more gap to save the engine. Sure it might rattle a little when cold and might have a little added oil in our evacuation systems but they lived and ran well.

So, I'm not new to these things, but I am new to a turbo application. Its added compression and combustion but no where near as violent as a nitrous system is in the cylinder. This is why I want to try it. This truck is going to be a race truck that's street driven sometimes. So it needs to be setup accordingly. As a race engine. It will be pushed one day, really hard. Which BTW, I did buy a Meth injection system this week, so that will help matters some. I didn't plan on it but it was a great deal, sooo.. done.

 

My specialty is daily drivers. Let me tell you from experience that there is a list of rules you MUST subscribe to in order to be successful with a daily driver. For example, a 0.0022" tri-metal bearing is NOT a daily driver friendly setting, just like too large of a ring gap, or the wrong clutch friction material, even the operating temperature range of the engine must be considered (usually 185-205*F) for daily service/economy/longevity. There is alot to be said for synthetic, lightweight oils (5W-30) and OEM style bearings/parts. Especially in the valvetrain, you want a very low lift lobe with a light spring, and a fuel cut rev limiter with headroom to spare. If you are interested in my complete list PM me

 

Ok, bringing this one back up for an update. I ended up having a couple of sleeves that wouldn't hone out. He cut them .003 and you can still feel the indention where it had water sitting in it for a while. It also looks like I am not doing a 100% SBE build and going for the list. Instead of trying to find another block I bought a set of 4.030 Diamond pistons that were on this site. I called Diamond and they were a custom build. I will be right above 10-1 compression with the 317 heads and LS9 gaskets. They were priced right and it gets my cylinders nice and clean.

Also when I talked to my machine shop he stated that he always sets the ring gaps between .006 and .007 times the bore for blown or turbo builds. He said he has done quite a few of these so that's good to know. So it sounds like he knows what he is doing. He also liked the idea of getting these new pistons with his knowing what I am trying to do. I hope to have the short block back in the next week or so.

 

Many lolz in here

I don't think many understand how much the top ring lengthens vs the second ring

Also no one even mentions ring material.... do you think a SS ring needs more than a steel?

Makes me lolz

 

^This. Ring material can have a big difference on how the ring acts when heated.

 

Why don't you post what your idea of a proper ring gap is. I plan to just run like 26/24 but I'd like to know why to run them at a certain gap not just because everyone else does it.

 

Lol because there is no magic number Jesus. You haven't even mentioned bore size or ring material